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From: ev_remove_this_ans@evans.pgh.pa.us (Arthur Evans Jr)
Newsgroups: comp.lang.ada
Subject: Re: Leap Seconds
Date: Tue, 29 May 2001 20:42:27 -0400
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References: <9elpii$30i$1@nh.pace.co.uk> <3B0ED67B.E40A4E06@averstar.com>
 <9f0ciq$itb$1@nh.pace.co.uk>
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Date: 2001-05-29T20:42:27-04:00
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In article <9f0ciq$itb$1@nh.pace.co.uk>, "Marin David Condic"
<marin.condic.auntie.spam@pacemicro.com> wrote:

> While a handful of seconds over a number of years may not be a big deal in
> most cases, I could easily imagine where they might make a difference.
> (Especially when trying to sync up with something else that is using a time
> base somewhere in the past and wondering if it counts the leap seconds and
> you don't. Source A counts them, source B doesn't and you're in the middle
> trying to figure out 'does anybody really know what time it is?')

I expect that an Ada program that communicates with an unmanned
(unpersoned?) space ship might care very much indeed.  Suppose the
ship sends a message from somewhere near Saturn or some such, the
message including a time stamp.  You can tell how far away from
earth it is by the difference between that time stamp and the time
the message is received.  You might care a lot about a 1-second
error.  (I assume an adequately accurate clock on the vessal.)

Here the problem is not one Ada can solve.  You would need a clock
at the receiving station that either was never corrected for leap
seconds, or you would need a table of corrections.  To put it
differently, you need some sort of clock at the receiving station
that tells you how much time has elapsed since the vessal was
launched.  Given that, an Ada program is easy, providing you have a
big enough field to store all those seconds.

Art Evans